T-square



HUGH 1r. GAHAN, or nnowna, i'sarrrsn COLUMBIA, canana.

T-SQ'U'ARE.

esa-tee.

Specification of Letters Patent.

Patented Oct. l,

Application filed January 19, 1926. Serial No. 352,588.

. To all whom it may concern:

such as a table top.

. A further object is to provide a T-square which does not-of necessity project beyond the end of the surface on which it is used.

The T-squaresat present in general use comprise a head and a blade, the head projecting below the lower surface of the blade so that its inner edge may bear against the edge of a drawing board. Such an arrangement has the disadvantage that a special board having a true guiding edge is necessary. It also has the disadvantage that in working on a large drawing board at a point remote from the guiding edge great difliculty is experienced in keeping the long T-square in proper parallelism. The ordinary T-square has the further disadvantage that its blade cannot be adjusted relatively to the guiding edge of the table so that it remains at 90 to the table edge. Many persons object to the adjustable blade T- squares as being both expensive and inaccurate.

According to the present invention a T- square is provided having the lower surfaces of its head and blade in the same plane and adapted to cooperate with a guide strip or straightedge which may be releasably secured to any part of a. table top or drawing board. The head and blade are preferably connected by a bridge leaving a space or groove in the under side of the blade exposing an edge of .the head for engagement with the straightedge.

In the drawings which illustrate the invention Figure 1 is a plan view of the device.

Figs. 2 to 6 inclusive are fragmentary, side elevations of a T-square illustrating various modifications of the present invention. 2

Referring more particularly to the drawings, 11 designates the head and 12 the blade of a T-square which, according to thisinvention, are preferably connected to a bridge 13 which locates the lower surfaces of the blade and head in the same plane. This bridge preferably supports the inner end 14 of the blade at some distance from the normal guiding edge 15 of the head so that a space 16 exists under the bridge for the reception of a guide strip or straightedge 17. The upper edge of the strip may be beveled as at 18 to give clearance for a drawing pen right up to the straightedge. This guide strip may be constructed in a number of ways as may also the T-square. In Figs. 1 and 3 the straightedge is illustrated as a simple strip of material, such as wood, 're cessed 19 in its upper surface to receive the heads of drawing tacks, the points of which project through the straightedge to secure the same to any suitable surface. In

Fig. 2 the straightedge 21 is illustrated as channelshaped in cross section and preferably formed of metal, the drawing tack 20 being used as before to secure the same to the working surface. In Fig. 4 the straightedge is illustrated as a simple strip of material having an attaching point or pin 22 which may be permanently connected thereto instead of in the manner shown in Figs. 2 and 3. It will be observed that in Figs. 1, 2 and f the guiding edge 15 of the T- square head bears against the straightedge,

that is to say, the straightedge is located in the space16'under the bridge. In Fig. 3 it will be observed that the groove 16 between the guiding edge of the head and the inner end of the blade has been replaced by a groove 23 formed in the lower surface of the head itself.

In Figs. 5 and 6 the head is grooved to receive a straightedge but in a slightly different manner from that shown in Fig. 3. In Fig. 5 the groove 24: is only large enough to receive the upturned edge of a guide strip 25 which'is L-shaped in cross section. This groove is formed from the lower surface of the head. In Fig. 6 a groove 26 is formed from the guiding edge of the head to receive the flange of a straightedge 27 which is Z-shaped in cross section.

The operation of the device is extremely simple. In all the forms the guide strip is releasably secured at any desired angle to the working surface and the head of the if-square slid along same in exactly the same manner as an ordinary IT-square is slid along the edge of a drawing board. On a large square for inserting details which can be.

drawing a draftsman may use a small T- shifted around the drawing as desired and also arranged at any desired angle on the drawing. A T-square according to this inventionis furthermore, not dependent on a true edge on the drawing board or table.

While various forms of the device have been shown in certain particular arrangements it will be understood that these details may be combined in any desired manner. For example, any of the forms of guide strip may be arranged to cooperate with the normal guiding edge of the head with the roove 23.

Ifaving thus described my invention, what I clalm 1s 2. In a 'lT-sourare, a head, a blade and a bridge, said head and blade being arranged with their lower surfaces in a single plane,

the blade being held by said bridge with its groove exposing an edge for coiiperation with the straight edge, a wall portion of the groove being recessed to receive the flange of the straight edge.

5. The combination with aflanged straight edge, of a T-square having the lower surface of its head and blade located in the same plane, said head and blade being spaced apart to define an intervening groove and to expose the inner edge of the head for cooperation with the straightedge, said inner edge being recessed to receive the flangeof the straight edge.

I In witness whereof I have hereunto set my hand.

HUGH N. GAHAN; 

